The present invention relates to a magnetic contactor(electromagnetic switch device) for star-delta connections, and more particularly to an electromagnetic switch device designed to be used for a star-delta starter adapted to start up a three-phase electric motor in order to allow the motor to be driven at its full speed within a short period of time.
As well known, star (Y)-delta (xcex94) starters, which are used to start up an electric motor, serve to establish a star connection for the electric motor upon the start-up of the electric motor, thereby reducing starting current and starting torque required in the start-up of the electric motor to a ⅓ level, while switching the connection for the electric motor into a delta connection after completion of the-start-up of the electric motor so that the electric motor is driven-in the delta connection state. Such star-delta starters are widely used in a variety of industrial fields in order to protect electric motors and peripheral devices thereof from overload.
Star-delta starters are classified into a contact type using an electromagnetic switch device adapted to switch electric contacts by use of electromagnets, and a non-contact type using a semiconductor switch device. The type using an electromagnetic switch device is more widely used.
FIGS. 1a, 1b and 2 illustrate a conventional electromagnetic switch device and a star-delta starter using the electromagnetic switch device, respectively. FIG. 1a is a perspective view illustrating the electromagnetic switch device, and FIG. 1b is a cross-sectional view taken along the line Axe2x80x94A of FIG. 1a. FIG. 2 is an equivalent circuit diagram illustrating the star-delta starter.
As shown in FIGS. 1a and 1b, the conventional electromagnetic switch device, which is denoted by the reference character C, includes a body 1, and a cover 2 separably attached to an upper surface 1a of the body 1. Three pairs of terminals 3 are disposed on the upper surface 1a of the body 1 in such a fashion that the terminals of each terminal pair are arranged at opposite sides of the body 1, respectively, while being insulated from one another. Electric power lines not shown are connected to the terminals 3, respectively. Isolating plates 4 are arranged at opposite sides of the cover 2 to isolate adjacent ones of the terminals 3.
Three pairs of fixed contacts 5 are also provided. Each fixed contact 5 is arranged at an end of an associated one of the terminals 3 extending toward a central portion of the body 1. The fixed contacts 5 are insulated from one another. A vertical moving member 6 is arranged at the central portion of the body 1 in such a fashion that it is upwardly and downwardly movable. Three pairs of moving contacts 7 insulated from one another are mounted to the vertical moving member 6 at opposite sides of the vertical moving member 6 in such a fashion that each of the, moving contacts 7 selectively comes into contact with an associated one of the fixed contacts 5 so that it is short-circuited or opened with respect to the associated fixed contact 5. A compression coil spring 8 is arranged around the vertical moving member 6 between the upper surface 1a of the body 1 and the moving contacts 7 in such a fashion that it always urges the vertical moving member 6 upwardly.
A fixed core 9 is arranged at a lower portion of the body 1. A coil 10 is wound around the fixed core 9 in order to form an electromagnet. Above the fixed core 9, a moving core 11 is arranged in such a fashion that it moves vertically along with the vertical moving member 6 in accordance with a magnetization of the electromagnet.
The conventional star-delta starter using electromagnetic switch devices having the above mentioned configuration includes an electromagnetic switch device C1 for a main circuit, an electromagnetic switch device C2 for a star circuit, and an electromagnetic switch device C3 for a delta connection, which are connected together as shown in the equivalent circuit diagram, of FIG. 2 and activated by a timer (not shown) to start up a three-phase electric motor M.
When current flows through the coil 10 of the electromagnetic switch device C2 for the star circuit upon starting the three-phase electric motor M, the electromagnet formed by the fixed core 9 and coil 10 is magnetized by virtue of the current.
Accordingly, the electromagnet generates a magnetic force greater than the resilience of the spring 8, so that the vertical moving member 6 and moving core 11 are downwardly moved. As a result, the moving contacts 7, which also move downwardly, come into contact with the fixed contacts 5, respectively.
When the electromagnetic switch device C1 for the main circuit is activated in accordance with the same procedure as mentioned above, a star connection is established for the three-phase electric motor M, so that the three-phase electric motor is started up using starting current and starting torque reduced to a ⅓ level. At the same time, the timer not shown begins to operate in order to count the drive time of the three-phase electric motor M.
After a predetermined period of time elapses, the current flowing through the coil 10 of the electromagnetic switch device C2 for the star connection is cut off by an operation of the timer. At the same time, current flows through the coil 10 of the electromagnetic switch device C3 for the delta connection.
In this state, the magnetic force of the electromagnet formed by the fixed core 9 and coil 10 of the electromagnetic switch device C2 for the star connection disappears. As a result, the vertical moving member 6 is upwardly moved along with the moving core 11 and moving contacts 7 by virtue of the resilience of the spring 8, thereby causing the moving contacts 7 to be separated from the fixed contacts 5.
Meanwhile, the electromagnet formed by the fixed core 9 and coil 10 of the electromagnetic switch device C3 for the delta connection is magnetized by virtue of the current flowing through the coil 10. As a result, the moving contacts 7 are downwardly moved, so that they come into contact with the fixed contacts 5, respectively.
Accordingly, the electromagnetic switch device C3 for the delta connection is short-circuited to electric power lines at its one-side terminals 3. As a result, the three-phase electric motor M is switched to the star connection state to a delta connection state, so that it is driven at a full speed.
In the star-delta starter having the above mentioned configuration, each of its electromagnetic switch devices is used only for a single purpose, that is, a star connection or a delta connection. For this reason, the conventional star-delta starter cannot implement a desired system unless at least two electromagnetic switch devices are used, even when those used for the main circuit are not taken into consideration.
As a result, the conventional star-delta starter involves high-manufacturing and installing costs and a large occupation space.
The conventional star-delta starter also involves a complex wiring for the connection between the electric motor and the electromagnetic switch device used. Such a complex wiring may result in a possibility of erroneous connections. In particular, such a wiring may be easily damaged by an external force applied thereto, thereby resulting in an erroneous operation of the starter or a damage of the electric motor.
Therefore, an object of the invention is to solve the above mentioned problems involved in the prior art, and to provide an electromagnetic switch device for star-delta connections which includes two electromagnets arranged in its body and two switching units operating in accordance with respective magnetization states of the electromagnets in order to selectively establish a star connection or a delta connection for a three-phase electric motor, so that it can reduce installation costs and an occupation space when it is applied to a star-delta starter while using no unnecessary wiring, thereby reducing erroneous connections and erroneous operations.
In accordance with the present invention, this object is accomplished by providing an electromagnetic switch device for star-delta connections comprising: a body; three power terminals arranged at one side of the body and respectively connected to three-phase power lines, the power terminals being insulated from one another; three main starting terminals arranged at the other side of the body and respectively connected to one-side terminals of a three-phase electric motor, the main starting terminals being insulated from one another; three star-delta terminals arranged at the other side of the body outside the main starting terminals and connected to the other-side ends of the three-phase electric motor, respectively, the star-delta terminals being insulated from one another; an electromagnet for a main circuit and an electromagnet for star-delta connections disposed at a lower portion of the body in such a fashion that they are laterally aligned with each other while being insulated from each other, each of the electromagnets including a fixed core and a coil wound around the fixed core; a main circuit switching unit arranged near the main circuit-end electromagnet in the interior of the body, the main circuit switching unit serving to selectively connect each of the main starting terminals to an associated one of the power terminals in accordance with a magnetization of the main circuit-end electromagnet; and a star-delta connection switching unit arranged near the star-delta connection-end electromagnet in the interior of the body, the star-delta connection switching unit serving to selectively connect the star-delta terminals to one another or to the main starting terminals, respectively, in accordance with a magnetization of the star-delta connection-end electromagnet.
Preferably, the electromagnetic switch device further comprises a timer arranged in the interior of the body and adapted to count an activation time of the main circuit-end electromagnet, thereby determining a point of time when the star-delta connection-end electromagnet is to be activated.
The electromagnetic switch device may further comprise isolating plates arranged between adjacent ones of the power terminals, between adjacent ones of the main starting terminals, and between adjacent ones of the star-delta terminals to isolate the adjacent power terminals, the adjacent main starting terminals, and the adjacent star-delta terminals, respectively.
The main circuit switching unit may comprise: a moving core vertically movable in accordance with a magnetization of the main circuit-end electromagnet; a vertical moving member integrally coupled to the moving core in such a fashion that it is moved along with the moving core; three pairs of fixed contacts arranged at desired positions within a vertical movement zone of the vertical moving member in such a fashion that the fixed contacts included in each of the fixed contact pairs are disposed at opposite sides of the vertical moving member, respectively, the fixed contacts arranged at one side of the vertical moving member being connected to the power terminals, respectively, while being insulated from one another, and the fixed contacts arranged at the other side of the vertical moving member being connected to the main starting terminals, respectively, while being insulated from one another; and three pairs of moving contacts mounted to the vertical moving member in such a fashion that the moving contacts included in each of the moving contact pairs are disposed at opposite sides of the vertical moving member, respectively, the moving contacts arranged at one side of the vertical moving member being insulated from one another, the moving contacts arranged at the other side of the vertical moving member being insulated from one another, and the moving contacts being vertically moved in accordance with a vertical movement of the vertical moving member, so that they selectively come into contact with respective associated ones of the fixed contacts, thereby causing the power terminal-end fixed contacts to be selectively connected to the starting terminal-end fixed contacts.
The star-delta connection switching unit may comprise: a moving core vertically movable in accordance with a magnetization of the star-delta connection-end electromagnet; a vertical moving member integrally coupled to the moving core in such a fashion that it is moved along with the moving core; three pairs of fixed contacts for star-delta connection arranged at desired positions within a vertical movement zone of the vertical moving member in such a fashion that the fixed contacts included in each of the fixed contact pairs are disposed at opposite sides of the vertical moving member, respectively, the fixed contacts arranged at one side of the vertical moving member being connected to the main starting terminals, respectively, while being insulated from one another, and the fixed contacts arranged at the other side of the vertical moving member being connected to the star-delta terminals, respectively, while being insulated from one another; three pairs of moving contacts for delta connection mounted to the vertical moving member in such a fashion that the moving contacts included in each of the moving contact pairs are disposed at opposite Sides of the vertical moving member, respectively, the moving contacts arranged at one side of the vertical moving member being insulated from one another, the moving contacts arranged at the other side of the vertical moving member being insulated from one another, and the moving contacts being vertically moved in accordance with a vertical movement of the vertical moving member, so that they selectively come into contact with respective associated ones of the fixed contacts, thereby causing the star-delta connection-end fixed contacts to be selectively connected to the starting terminal-end fixed contacts so as to achieve a delta connection; and three moving contacts for star connection mounted to the vertical moving member at a position vertically shifted from the delta connection-end moving contacts near the star-delta connection-end fixed contacts, the star connection-end moving contacts being short-circuited together, and the star connection-end moving contacts being vertically moved in accordance with a vertical movement of the vertical moving member, so that they selectively come into contact with respective associated ones of the fixed contacts, thereby causing the fixed contacts to be selectively connected together so as to achieve a star connection, the star connection by the star connection-end moving contacts being achieved when the delta connection by the delta connection-end moving contacts is released.
Each of the main circuit switching unit and star-delta connection switching unit may further comprise a return springs adapted to provide a return force for returning the associated vertical moving member to an original position thereof at which the associated moving contacts are separated from respective associated ones of the fixed contacts.
Each of the main circuit switching unit and star-delta connection switching unit may further comprise an arc prevention spring arranged in the associated vertical moving member and adapted to always urge the associated moving contacts toward the associated fixed contacts, thereby increasing the contact force of the moving contacts when the moving contacts come into contact with the fixed contacts, so as to suppress generation of arc at regions where the moving contacts come into contact with the fixed contacts, respectively.